1. Field of the Invention
This invention relates to an automobile heating apparatus and a heat generator for the same.
2. Description of the Prior Art
One of the prior arts in the field of automobile heating apparatus is set forth in Japanese Unexamined Utility Model Publication No. 121476/1984.
As illustrated in FIG. 3, in the prior art automobile heating apparatus, the heat is exchanged between the high temperature exhaust gas and the cooling water by way of a heat exchanger when cold-starting the engine or travelling normally in a cold district, namely when the engine cooling water flowing in the hot water circuit for heating has not been heated sufficiently. Whereby the cooling water flowing in the hot water circuit for heating is heated in order to improve the heating capacity.
To be more precise, the heat of the high temperature exhaust gas flowing in an exhaust pipe 51 is absorbed by a heat absorbing portion 52a of a heat exchanger 52 disposed in the exhaust pipe 51. The absorbed heat is then radiated to the cooling water flowing in a hot water circuit 53 for heating by a heat radiating portion 52b of the heat exchanger 52. The cooling water flowing in the hot water circuit 53 for heating is heated accordingly, and delivered to a heating apparatus 54.
However, in the prior art automobile heating apparatus, the effective heat transfer area of the heat absorbing portion 52a of the heat exchanger 52 should be made large in order to attain a predetermined heating capacity, because the thermal conductivity of the gas, i.e., the exhaust gas is smaller than the thermal conductivity of the liquid, i.e., the cooling water by a factor of several tens. But, when a large heat absorbing portion 52a of the heat exchanger 52 is disposed in the exhaust pipe 51, the exhaust pipe 51 comes to have a sharply reduced area for flowing the exhaust gas. There accordingly arise fears for the clogged exhaust pipe 51 due to soot, the reduced engine output or engine troubles due to the increasing back pressure applied to the engine. In addition, the heat exchanger 52 should be enlarged as a whole when enlarging the heat absorbing portion 52a, and it has been troublesome to install the thus enlarged heat exchanger 52 on automobiles.